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Abstract

Tapered optical fibers offer easy access to the evanescent field of their guided modes which is ideal for sensing applications. We introduce a soft-landing technique utilizing a linear Paul trap to select and place a single microparticle on the surface of a tapered optical fiber. This approach allows on-demand functionalization of fragile nanophotonic components with arbitrary particles, e.g., for advanced nanosensors.

Figures (7)

(Color online) Schematic of the Paul trap: The trap consists of two rf-electrodes and two dc-electrodes. The dc-electrodes are subdivided into twelve segments with lengths of 2, 5 and 7mm. The total length of the trap is 70mm. Segments 1–3 constitute the spectroscopy region, where the fluorescence measurements and the deposition on the optical fiber taper are performed. Loading of the trap occurs from the righthand side (segments 10–12.) The segmentation allows confinement of several particles at once, isolation of single particles, and their transfer within the trap.

(Color online) Schematic of optical setup: solid (green) and dashed (red) lines indicate the optical paths for the excitation laser and fluorescence detection, respectively. By flipping either mirror FM1 or FM2 it is possible to excite and detect particles hovering in the trap through the microscope objective or to measure deposited particles directly through the optical fiber taper. FM3 allows measurement of the change in transmission via a photodiode as a particle is placed onto the taper.

(a) Fluorescence spectrum of a dye-doped particle trapped in the spectroscopy region of the Paul trap collected by the microscope objective, (b) spectrum of the same particle after deposition onto a fiber taper of 700nm in diameter collected via the same fiber. The excitation power was Pext=30µW at 514nm.

(a) Decrease in transmission at 532nm while landing a single 1.5µm-sized particle consisting of a cluster of polystyrene beads on a 850nm diameter taper. The transmission is normalized to the transmission through the taper before the particle is placed (corresponds to 1.0). The value of 0 corresponds to the transmitted signal when the laser is turned off. (b) Microscope image of the landed particle.

(Color online) Results of FDTD simulation for the transmission for the HE11 mode at 532nm in a glass cylinder dt=850nm of length 100µm piercing a polystyrene sphere of diameter ds. The transmission through the glass cylinder is given by the time averaged Poynting vector integrated across the end facet of the cylinder and normalized by the power of the seeded mode. The unit cell size of the simulation is 33nm and perfectly matched layers are used as boundary condition.